This invention relates to a method of separating aluminum or aluminum alloys from an article composed of an aluminum or aluminum alloy part bonded to a ferrous metal part and, in one aspect, to a method for reclaiming cast iron cylinder sleeves from aluminum cylinder blocks for internal combustion engines.
Various articles include an aluminum or aluminum alloy part bonded to a ferrous metal part. For example, cylinder blocks for internal combustion engines commonly are formed by die casting an aluminum alloy around wear-resistant, cast iron cylinder sleeves. When such blocks are rejected during manufacture because a failure to meet quality control requirements or salvaged for scrap, it is desirable to reclaim both the aluminum alloy and the cast iron sleeves. Two types of procedures have been used in the past for this purpose.
In one type procedure, the cylinder block is heated to the temperature above the melting point of the aluminum alloy and tumbled, vibrated or otherwise mechanically agitated until the sleeves are separated from the block.
In another type procedure, the cylinder block is placed in a furnace and heated to a temperature above the melting point of the aluminum alloy and the molten aluminum flows from the sleeves. Aluminum forms a tenacious bond with the cast iron sleeves and cannot be completely removed by melting alone with this procedure. The amount of aluminum remaining on the sleeves varies depending upon the aluminum alloy composition, the melting temperature used, etc., and a separate treatment, such as leaching with a caustic solution, is required to remove all the aluminum. In addition to the added cost and time required for this removal treatment, the aluminum removed during this step cannot be economically recovered. If the sleeves are suitable for reuse, the melting temperature must be kept below a predetermined level in order to prevent damage to the sleeves. Consequently, it often is difficult to control the temperature at a level which facilitates maximum removal of the aluminum without causing deterioration of the metallurgical properties of the sleeves.
It is known to use molten salt baths for recovering aluminum form various substances. For example, the Robinson U.S. Pat. No. 1,180,435, issued April 25, 1916, relates to the use of a molten bath of sodium chloride and cryolite for recovering aluminum from metal-bearing substances containing aluminum in its elemental state. The Burkhardt U.S. Pat. No. 2,787,592, issued Apr. 2, 1957, relates to the use of a molten salt bath for recovering aluminum from aluminum base scrap metals containing a heavier metal. The bath has a specific gravity higher than aluminum, but lower than the heavier metal, causing the molten aluminum to float. The Wainer U.S. Pat. No. 3,000,766, issued Sept. 19, 1961, relates to the use of a molten bath of an alkali metal nitrite, at a temperature below the melting point of aluminum, for separating organic non-metallic materials from aluminum. The Racunas et al U.S. Pat. No. 3,846,123, issued Nov. 5, 1974, relates to the use of a mechanically agitated molten salt bath for separating aluminum from non-metallic solids.
None of these patents relate to the use of a molten salt bath for separating aluminum from a article composed of an aluminum part bonded to a ferrous metal part in a manner whereby substantially all the aluminum is removed from the ferrous metal during the melting step.